Re: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels

"Templin, Fred L" <Fred.L.Templin@boeing.com> Mon, 11 October 2010 17:12 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: =?iso-8859-1?Q?R=E9mi_Despr=E9s?= <remi.despres@free.fr>
Date: Mon, 11 Oct 2010 10:13:43 -0700
Thread-Topic: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels
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Cc: Softwires <softwires@ietf.org>, "v4tov6transition@ietf.org" <v4tov6transition@ietf.org>
Subject: Re: [v4tov6transition] IPv6 VPNs configured over 1280 MTU tunnels
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Remi, 

> -----Original Message-----
> From: Rémi Després [mailto:remi.despres@free.fr] 
> Sent: Monday, October 11, 2010 10:05 AM
> To: Templin, Fred L
> Cc: Washam Fan; Softwires; v4tov6transition@ietf.org
> Subject: Re: [v4tov6transition] IPv6 VPNs configured over 
> 1280 MTU tunnels
> 
> 
> Le 11 oct. 2010 à 18:42, Templin, Fred L a écrit :
> 
> >> ...
> >> Actually, the 6a44 specification should, instead of 1280, 
> >> require IPv4 MTU - 28 octets, both for hairpinning and 
> >> traversal cases.
> > 
> > How can you be sure that IPv4 PMTUD will work in
> > the traversal case?
> 
> In the to-host direction, because the ISP network is all what 
> is left to traverse before reaching the CPE.

In what you call the to-host direction, any ICMPv4
returned from the ISP network might not have enough
information for stateless translation to ICMPv6.

> In the from host direction, one can't be sure, but doesnt' need to.
> If a smaller PMTU is encountered further downstream, a PTB 
> ICMPv6 error message will be returned from there.

In the from-host direction, any ICMPv4 returned from
the ISP network might not be delivered to the tunnel
endpoint due to NAT filtering, and might not have
enough information for stateless translation to ICMPv6.

Fred
fred.l.templin@boeing.com

> RD